51 lines
1.9 KiB
Java
51 lines
1.9 KiB
Java
/* Copyright (C) 2023-2024 Petr Kadlec
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This file is part of Gadgetbridge.
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Gadgetbridge is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published
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by the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Gadgetbridge is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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package nodomain.freeyourgadget.gadgetbridge.service.devices.garmin;
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import java.nio.ByteBuffer;
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public final class ChecksumCalculator {
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private static final int[] CONSTANTS = {
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0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401,
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0xA001, 0x6C00,0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400
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};
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private ChecksumCalculator() {
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}
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public static int computeCrc(byte[] data, int offset, int length) {
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return computeCrc(0, data, offset, length);
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}
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public static int computeCrc(ByteBuffer byteBuffer, int offset, int length) {
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byteBuffer.rewind();
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byte[] data = new byte[length];
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byteBuffer.get(data);
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return computeCrc(0, data, offset, length);
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}
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public static int computeCrc(int initialCrc, byte[] data, int offset, int length) {
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int crc = initialCrc;
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for (int i = offset; i < offset + length; ++i) {
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int b = data[i];
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crc = (((crc >> 4) & 4095) ^ CONSTANTS[crc & 15]) ^ CONSTANTS[b & 15];
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crc = (((crc >> 4) & 4095) ^ CONSTANTS[crc & 15]) ^ CONSTANTS[(b >> 4) & 15];
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}
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return crc;
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}
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}
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